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OCR B A Level Chemistry > Developing Fuels > Flashcards

Flashcards in Developing Fuels Deck (42)
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1

Define enthalpy change of reaction.

The amount of energy given out/taken in during a reaction

2

What are exothermic reactions?

Reactions that give out energy to the surroundings, meaning they heat up.
ΔH is negative- energy to form bonds is greater than energy needed to break the bonds

3

What are endothermic reactions?

Reactions that take in energy from the surroundings, making them cool down.
ΔH is positive- energy to form bonds is less than energy needed to break the bonds

4

How do you work out ΔH?

ΔH=H(products)-H(reactants)

5

Define the system of a reaction.

The products and the reactants that chemists are interested in

6

What are a reaction's surroundings?

The rest of the world, like the test tube, air etc

7

What are standard conditions?

298K (25°C), 1 atm, 1 mol dm^-3, standard states (solid, liquid, or gas)

8

Define standard enthalpy change for a reaction.

The enthalpy change of a reaction when molar quantities of reactants react together under standard conditions in standard states

9

Define standard enthalpy of combustion

The enthalpy change that occurs when one mole of reactant completely burns in oxygen in standard states under standard conditions

10

Define standard enthalpy of formation

The enthalpy change when one mole of a compound is formed from its elements under standard conditions in standard states

11

Define standard enthalpy of neutralisation

The enthalpy change one one mole of H+ ions react with one mole of OH- ions to form one mole of water

12

Energy transferred=

Specific heat capacity x mass x temperature change

13

What is Hess's law?

The enthalpy change for any chemical reaction is independent of the intermediate stages, so long as the initial and final conditions are the same

14

What is the overall formula to determine the enthalpy change?

ΔH1 = ΔH2 -ΔH3

15

What is fractional distillation?

The method of separating hydrocarbons according to chain lengths

16

State the general formula of alkanes

C(n)H(2n+2)

17

How do you identify aromatic molecules?

Molecules with one or more benzene rings

18

What are aliphatic molecules?

Molecules that don't have any benzene rings

19

Hydrocarbons with no double/triple bonds are...

saturated

20

Hydrocarbons with double bonds are...

unsaturated

21

How do you name hydrocarbons?

1) Name the longest carbon chain
2) Identify any side chains and name them
3) Identify the location of the side chains. Use the lowest number possible
4) List the side chains alphabetically

22

Define energy density

How much energy you can get per kilogram of fuel

23

What is the formula for energy density?

100 x (standard enthalpy/molecular mass)

24

Why is it difficult to measure exact bond enthalpies?

The exact value depends on the particular compound in which the bond is found

25

Why is bond breaking endothermic?

It requires energy

26

Why is bond making exothermic?

It releases energy

27

Give two reasons why theoretical calculations are different to experimental data

1) Bond enthalpies found in tables are averages from several compounds
2) Products/reactants aren't in their standard states

28

What is cracking?

Any reaction where a larger molecule is made into smaller molecules. In terms of hydrocarbons, normally long chain alkane --> shorter chain alkane + alkene

29

What are catalysts?

Chemicals that speed up reactions by providing an alternative pathway with a lower activation enthalpy, and are chemically unchanged at the end of the reaction

30

Why is catalyst poisoning an issue?

The catalyst becomes inactive because a substance stops it from functioning properly, leading to reduced reactivity